Foaming agents, or blowing agents, are widely used in the polyurethane industry. Although many compounds have been proposed as suitable blowing agents for polyurethane manufacture, relatively few of these are commonly used. The most widely used blowing agents have been freon (CFC-11, a chlorofluorocarbon) and dichloromethane (methylene chloride). Although freon and dichloromethane are excellent blowing agents for various polyurethane applications, there is great interest in finding replacements. CFCs are harmful to the earth's upper ozone layer, so production of these is being phased out worldwide. A small portion of the market now uses HCFCs or water instead of CFCs. Unfortunately, HCFCs are expensive and still contribute to ozone depletion. Polyurethane foams blown only with water have been developed, but good physical properties and low densities are often difficult to achieve without an auxiliary blowing agent. Formulators concerned about the toxicity of methylene chloride continue to search for satisfactory alternatives.
Diethyl ether has been listed as a blowing agent for polyurethane foams (see, for example, U.S. Pat. Nos. 4,546,122 and 4,764,541), but actual examples of foams made with diethyl ether are hard to find. The flammability of diethyl ether and its high volatility have probably dissuaded those skilled in the art from actually using it.
Tertiary aliphatic ethers such as methyl tert-butyl ether (MTBE) and tert-amyl methyl ether (TAME) are industrially important as an octane enhancers for gasoline. Tertiary ethers have not been previously shown to be effective blowing agents for polyurethane foams.